The present invention generally relates to a container for holding substrates and more particularly, relates to a wafer cassette for holding wafers for transporting in a semiconductor fabrication facility wherein the cassette has dividers of different length or color such that cross-slot misplacement of wafers by an operator can be avoided.
In the fabrication process for semiconductor devices, wafers of a semiconducting material are processed in various processes in which a plurality of wafers are frequently processed simultaneously. For instance, in a low pressure chemical vapor deposition (LPCVD) reactor, a large number of wafers can be processed in each run. The wafers are stacked side by side with only a few millimeters apart in a quartz reaction tube. The quartz reaction tube, sometimes called wafer boats, can hold up to 200 wafers. When the wafers are held vertically and separated from each other by a narrow space, a maximum wafer capacity can be achieved in a reaction chamber. For instance, wafers can be positioned in a diffusion or oxidation furnace wherein the wafers are placed perpendicular to a gas flow in a circular cross-sectioned quartz tube.
When a reactor is designed for a specific process, the geometry of the reactor is dictated by the pressure source and the energy source utilized in the reactor. The geometry of the reactor is also an important factor in the through-put rate of the reactor. In general, the reactor should be designed such that an equal flow of reactants can be delivered uniformly to each wafer. It is therefore more desirable to stack the wafers horizontally by laying them flat on a horizontal surface instead of stacking vertically at close spacing, even though the horizontal lay out is more susceptible to contamination by falling particles.
A vertical furnace operates essentially in the same manner as a horizontal furnace, except for the orientation of the wafers. In a vertical furnace, the wafers are loaded into a horizontal position by a wafer tweezer from a wafer cassette in which the wafers are stored or transported between processing stations. A wafer tweezer, or a wafer paddle that is utilized for transporting wafers into process machines from a wafer cassette is normally constructed of a quartz material that is capable of withstanding high temperature and corrosive environments. The wafer cassette, on the other hand, is normally constructed of a plastic material that is basically a container which has an open front and corrugated sidewalls formed by dividers for separating the wafers stored therein. The wafer cassette can be advantageously injection molded of a plastic material for accommodating a specifically sized substrate, i.e., a six inch or an eight inch wafer. A typical wafer cassette is shown in FIG. 1.
The wafer cassette 10, as shown in FIG. 1, is constructed by a top wall 12, a bottom wall 14, a back wall 16, and sidewalls 18 and 22. A cavity 24 is defined by the walls which also provides a front opening 26. On the interior surfaces 28 and 32 of the sidewalls 18 and 22, a corrugated configuration is formed by a plurality of dividers 34 and 36. The dividers 34, 36 are formed in ridge-shape that are oriented parallel with the bottom wall 14 and perpendicular to the rear wall 16. Slot-shaped openings, or receptacles 38, 42 are formed by the dividers 34 and 36. The dividers 34 and 36 are formed in a suitable length and thickness such that an electronic substrate, e.g., a wafer can be easily slid thereinto.
Since the wafer cassette 10 is used to store wafers between various fabrication processes and to transport wafers between various processing stations, the wafers contained therein are frequently inspected by an operator either for quality reasons or for identification of the wafer lots. When a wafer 20 is taken out of the cassette 10 and then manually put back in, human error frequently occurs which results in a wafer misplacement, i.e., a cross-slot placement of the wafer 20 as shown in FIG. 2. The cross-slot misplacement of a wafer into a wafer cassette occurs due to the large number of dividers on the sidewalls of the wafer cassette and the difficulty of identifying corresponding pairs of dividers on the opposite sidewalls of the cassette. The likelihood of making such mistakes is also contributed by the fact that the cassette is normally molded of a black plastic material.
When a cross-slot misplacement of wafer by an operator occurs, serious consequences can result when an automated wafer loader is used to unload the wafer from the cassette. For instance, when a wafer tweezer or paddle is used to unload wafers from a SMIF (standard mechanical interface machine) apparatus, the tweezer blade or paddle collides with the wafer that is misplaced resulting either in the breakage of wafer, a damage to the machine or both. In either event, the result can be catastrophic in lost wafer or machine down time. In using the presently available conventional wafer cassettes, the cross-slot misplacement of wafers by an operator cannot be avoided.
It is therefore an object of the present invention to provide a wafer cassette for holding wafers that does not have the drawbacks and shortcomings of the conventional wafer cassettes wherein wafers can be misplaced in the cassette.
It is another object of the present invention to provide a wafer cassette that is equipped with dividers on the sidewalls which are easily identifiable in matched pairs on the opposite sides of the wafer cassette cavity.
It is a further object of the present invention to provide a wafer cassette that is equipped with dividers which are fabricated of different colors such that corresponding pairs of the dividers on the opposite sidewalls of the cassette can be easily identified to avoid the cross-slot misplacement of the wafers by an operator.
It is another further object of the present invention to provide a wafer cassette that is equipped with dividers which are fabricated in different length in alternating orders such that corresponding pairs of the dividers on the opposite sidewalls of the cassette can be easily identified to facilitate the correct placement of wafers therein by an operator.
It is still another object of the present invention to provide a wafer cassette that is equipped with dividers on the opposite sidewalls of the cassette which are molded of at least two different colors in corresponding pairs such that a correct pair of dividers can be easily identified by an operator when manually inserting a wafer into the cassette.
It is yet another object of the present invention to provide a wafer cassette that is equipped with dividers which are ridge-shaped on the opposite sidewalls of the cassette that are of a thickness and a length sufficient for holding securely a wafer therein.
It is yet another further object of the present invention to provide a wafer cassette that is equipped with dividers located on the opposite interior sidewalls of the cassette that have at least two different lengths or colors in corresponding pairs for easy identification by an operator when inserting a wafer therein.
It is still another further object of the present invention to provide a wafer cassette that is equipped with dividers on the opposite interior sidewalls of the cassette which are made of different lengths between about 0.5 cm and about 2 cm with the oppositely positioned dividers on the two sidewalls being of the same length.
In accordance with the present invention, a container for holding electronic substrates that is equipped with dividers on the opposing interior sidewalls for holding the substrates which are of different lengths or colors in corresponding pairs is provided.
In a preferred embodiment, a container for holding substrates is provided which consists of a body that has a top wall, a bottom wall, a rear wall and two sidewalls forming an enclosure having a front opening and defining a cavity contained therein, a left sidewall and a right sidewall each having a corrugated interior surface, a first plurality of ridge-shaped dividers forming the corrugated interior surface on the left sidewall each having a base portion integral with the sidewall and a tip portion extending outwardly from the sidewall toward the cavity in the body, the ridge-shaped dividers are oriented parallel to the bottom wall and perpendicular to the rear wall defining slot-shaped receptacles thereinbetween, a second plurality of ridge-shaped dividers forming the corrugated interior surface on the right sidewall each having a base portion integral with the sidewall and a tip portion extending outwardly from the sidewall toward the cavity in the body, the ridge-shaped dividers are oriented parallel to the bottom wall and perpendicular to the front opening defining slot-shaped receptacles thereinbetween, each of the first and the second plurality of ridge-shaped dividers has a length and a thickness that are sufficient to support a substrate thereon without the occurrence of a substrate falling out of the receptacles or of contacting substrates immediately above or below the substrate, and each of even numbered dividers in the first and the second plurality of dividers appears different to an operator than each of odd numbered dividers wherein the even or odd numbered dividers are counted from the bottom-most divider.
The substrates held in the container are electronic substrates such as silicon wafers. The container can be advantageously used as a wafer cassette for transporting wafers in a semiconductor fabrication plant. The even numbered dividers in the first and the second plurality of dividers may have a different color than the odd numbered dividers. The even numbered dividers in the first and the second plurality of dividers may also have a different length than the odd numbered dividers. The first and the second plurality of ridge-shaped dividers are provided alternatingly in at least two different colors with the oppositely positioned dividers on the left and the right sidewalls being of the same color. The first and the second plurality of ridge-shaped dividers may also be provided alternatingly in at least two different lengths with the oppositely positioned dividers on the left and the right sidewalls being of the same length.
In another preferred embodiment of the present invention, a wafer cassette is provided which includes a cassette body which has a top wall, a bottom wall, a rear wall and two sidewalls forming an open-front enclosure and defining a cavity therein, a left sidewall and a right sidewall each having a corrugated interior surface, a first plurality of ridge-shaped dividers forming the corrugated interior surface in the left sidewall each having a base portion integral with the sidewall and a tip portion extending outwardly from the sidewall into the cavity in the body, the ridge-shaped dividers are oriented parallel to the bottom wall and perpendicular to the front opening defining slot-shaped receptacles thereinbetween, a second plurality of ridge-shaped dividers forming the corrugated interior surface on the right sidewall each having a base portion integral with the sidewall and a tip portion extending outwardly from the sidewall into the cavity in the body, the ridge-shaped dividers are oriented parallel to the bottom wall and perpendicular to the front opening defining slot-shaped receptacles thereinbetween, each of the first and the second plurality of ridge-shaped dividers has a length and a thickness that are sufficient to support a substrate thereon without the occurrence of a substrate falling out of the receptacles or of contacting substrates immediately adjacent to the substrate, and the first and the second plurality of ridge-shaped dividers are provided alternatingly in at least two different colors with the oppositely positioned dividers on the left sidewall and the right sidewall being of the same color. The at least two different colors are provided in sufficient distinction for detection by human eyes. The at least two different colors may be provided in two distinctly different colors. The at least two different colors may be three distinctly different colors. Suitable different colors may be blue and white, or black and white.
In yet another preferred embodiment of the present invention, a wafer cassette for loading of wafers without the cross-slot misplacement problem is provided which includes a cassette body that has a top wall, a bottom wall, a rear wall and two sidewalls forming an open-front enclosure and defining a cavity therein, a left sidewall and a right sidewall each has a corrugated interior surface, a first plurality of ridge-shaped dividers forming the corrugated interior surface in the left sidewall each has a base portion integral with the sidewall and a tip portion extending outwardly from the sidewall toward the cavity in the body, the ridge-shaped dividers are oriented parallel to the bottom wall and perpendicular to the rear wall defining slot-shaped receptacles thereinbetween, a second plurality of ridge-shaped dividers forming the corrugated interior surface on the right sidewall each has a base portion integral with the sidewall and a tip portion extending outwardly from the sidewall toward the cavity in the body, the ridge-shaped dividers are oriented parallel to the bottom wall and perpendicular to the front opening defining slot-shaped receptacles thereinbetween, each of the first and the second plurality of ridge-shaped dividers has a length and a thickness that are sufficient to support a substrate thereon, and the first and the second plurality of ridge-shaped dividers are provided alternatingly in at least two different lengths with the oppositely positioned dividers on the left and the right sidewalls of the same length. The at least two different lengths are determined as the distance between the base portion and the tip portion of the dividers. The at least two different lengths are selected between about 0.5 cm and about 2 cm. The at least two different lengths are also selected such that they are easily distinguishable by human eyes. The at least two different lengths are lengths preferably selected between about 1 cm and about 2 cm.